This invention relates to a pushbutton switch element for a pushbutton switch structure used for electronic equipment, a portable terminal, an automobile component or the like, and more particularly to a pushbutton switch element for a pushbutton switch structure suitable for use for equipment such as a power window switch for an automobile or the like which is required to carry out an on-off operation of an electric circuit thereof in a multistage manner while generating a click in a multistage manner which is felt by a user.
A mechanical switch has been conventionally used as a switch which generates a click in a multistage way or manner which is felt by a user. Such a mechanical switch is constructed in such a manner as shown in FIG. 7A by way of example. There is also known another conventional mechanical switch which is constructed as shown in FIG. 8.
The conventional mechanical switch shown in each of FIGS. 7A and 8 is typically used for an electronic instrument such as an electronic piano, a power window switch for an automobile or the like so as to generate a click which is felt by a user or carry out electrical connection in a multistage manner.
The conventional mechanical switch generally designated by reference numeral 101 in FIG. 7A includes a housing 101a, a leaf spring 101b, a pressing force transmission member 101c, a spring 101d, a lead frame 101e and a base plate 101f. The leaf spring 101b is provided with a projection 101b.sub.1 and the pressing force transmission member 101c is provided with two recesses 101c.sub.1 and 101c.sub.2. Locked fitting of the projection 101b.sub.1 of the leaf spring 101b in each of the recesses 101c.sub.1 and 101c.sub.2 of the pressing force transmission member 101c permits slide resistance or friction resistance between the leaf spring 101b and the pressing force transmission member 101c to be different from that therebetween obtained when the locked fitting is not carried out, so that the mechanical switch may generate a click which is felt by a user. The mechanical switch of FIG. 7A thus constructed exhibits a load curve shown in FIG. 7B, wherein a point F.sub.1 indicates a click generated during first fitting of the recess 101c.sub.1 on the projection 101b.sub.1 and a point F.sub.2 indicates a click generated during second fitting of the recess 101c.sub.2 on the projection 101b.sub.1.
The conventional mechanical switch 102 generally designated by reference numeral 102 in FIG. 8 includes a housing 102a, a frame 102b, a slide member 102c made of a plastic material, a spring 102d made of metal, plungers 102e, a cover member 102f made of an elastomer material, a key top 102g made of a resin material and a base plate 102h. Thus, the mechanical switch 102 is constituted by seven members made of plastic materials, the metal spring and the base plate to generate a click like that of the mechanical switch 101 described above. In the mechanical switch 102, mechanical locking among the plastic members by fitting permits the mechanical switch 102 to generate a click which is felt by a user due to resistance to movement among the members. The mechanical switch 102 exhibits substantially the same load curve as that shown in FIG. 7B.
In addition, there is used a press switch which is made of a silicone rubber material and constructed so as to generate a click in a multistage manner which is felt by a user. In general, a pushbutton switch made of a silicone rubber material attains a switching operation while being reduced in the number of parts, resulting in it being commonly used for a variety of pushbutton switch equipment such as an electronic calculator, a word processor, a remote controller and the like.
Now, a conventional pushbutton switch cover made of a silicone rubber material and adapted to be used for a word processor will be described with reference to FIGS. 9A and 9B.
A pushbutton switch cover 103 for a pushbutton switch structure is integrally formed so as to generate a click in a two-stage manner which is felt by a user and made of a rubber-like elastic material represented by silicone rubber. In FIG. 9A, only one pushbutton switch is illustrated. The pushbutton switch cover 103 includes a cylindrical rib 103a arranged so as to be positioned at a top of the pushbutton switch, a first dome-like section 103b for generating a first click at a point F.sub.1 (FIG. 9B), a second dome-like section 103c of a thin wall arranged at a central position of the pushbutton switch so as to generate a second click at a point F.sub.2, and a projection 103b.sub.2 formed so as to downwardly project from a ceiling of the second dome-like section 103c and provided on a lower surface thereof with a contact 103b.sub.1. The rib 103a and thin-wall dome sections 103b and 103c are flexed in order by pressing a pushbutton, to thereby generate a click in a two-stage manner which is felt by a user. The pushbutton switch thus constructed is mainly used for a key board for a word processor intended to prevent thecitis.
In the past, a switch such as a power window switch for an automobile or the like which is demanded not only to exhibit two or more switching functions but to generate an enhanced click which is felt by a user (a click ratio being typically as high as 30% or more) generally is necessarily required to use a mechanical switch (tactile switch) mechanism which utilizes slide resistance due to a combination of functional parts. Also, the mechanical switch shown in FIG. 8 is increased in the number of parts and complicated in structure, to thereby cause generation of rebound sound or contact sound during sliding of the parts and returning of the button, as well as resonance sound due to external vibration such as vibration of an engine of an automobile. Also, a so-called rubber switch such as the switch shown in FIG. 9A which exhibits two or more conductive functions fails to generate a click sufficient to permit a user or operator to recognize turning-on of the switch carried out twice by the feel.
This is due to the fact that the click is generated only by both deformation and restoration of the rib 103a and dome sections 103b and 103c which are made of a thin-wall rubber-like elastic material. In other words, this is due to the fact that the click is generated by impact resilience of the elastic material and restriction of a configuration of the dome sections determined depending on a material therefor.